1. Technical Field
Disclosed are methods for hardening pump casings and, more specifically, methods for hardening vane pump casings The disclosed methods are particularly useful for the design and manufacture of stainless steel rotary vane pumps Wear of vane pump casings is reduced resulting in less material being removed from the casing and less material being embedded into the vanes and/or causing premature weal of the vanes
2. Description of the Related Art
Vane pumps are used successfully in a wide variety of applications and industries. Because of vane strength and the absence of metal-to-metal contact, vane pumps are ideally suited for low-viscosity, nonlubricating liquids up to 2,200 cSt/10,000 SSU. Such liquids include LPG, ammonia, solvents, alcohol, fuel oils, gasoline, and refrigerants. Vane pumps are available in a number of vane configurations including sliding vanes, flexible vanes, swinging vanes, rolling vanes, and external vanes. Vane pumps are noted for their reliability, dry priming, easy maintenance, and good suction characteristics. Moreover, the vanes can usually handle fluid temperatures ranging from −32° C. (−25° F.) to 260° C. (500° F.) and pressures up to 30 BAR (400 PSI).
Each type of vane pump offers unique advantages For example, external vane pumps can handle large solids. Flexible vane pumps, on the other hand, can only handle small solids but create good vacuum Sliding vane pumps can run dry for short periods of time and handle small amounts of vapor.
As shown in FIGS. 1-3, a vane pump 10 typically includes a slotted rotor 11 eccentrically supported within a cycloidal chamber 12 of a casing 13. The rotor 11 is located close to the wall of the casing so a crescent-shaped cavity 14 is formed. The rotor 11 is sealed in the chamber by two side discs (not shown in FIGS. 1-3). Vanes 15 fit within the slots of the rotor 11. As the rotor 11 rotates and fluid enters the pump 10, centrifugal force, hydraulic pressure, and/or pushrods push the vanes 15 to the walls of the casing 13 Fluid enters the pockets created by the vanes 15, rotor 11, casing 13, and discs. As the rotor 11 continues to rotate, the vanes 15 sweep the fluid to the opposite side of the crescent cavity 14 where it is squeezed through discharge holes 16 of the casing to the discharge port 17.
On problem associated with vane pumps having steel casings is casing weal Specifically, contact between the vanes and the casing wall results in removal of material from the casing wall, which enters the fluid flow, can become embedded in the vanes and/or cause premature vane wear Also, fluid contamination caused by casing material can be problematic as well. Therefore, development of improved casings for vane pumps is needed, including improvements in steel casings, more specifically, stainless steel casings and still more specifically, austenitic stainless steel casings.